Capacitance discharge (CD) ignition systems are widely used in internal combustion engines, such as in automotive and industrial applications, to provide energy to the engine spark plugs. The construction and operation of conventional capacitance discharge systems is well known, and is discussed only briefly herein for an understanding and appreciation of the present invention.
A conventional capacitance discharge ignition system typically includes sensors such as variable reluctance sensors that provide signals indicative of crankshaft position relative to top dead center (TDC) of the #1 cylinder and engine speed, an electric power source, means to convert the supply voltage from the power source to a relatively high voltage, a capacitor to store energy from the power source, means to control the voltage on the energy storage capacitor, and timing means to process information from the sensors to determine when the stored energy should be discharged into an ignition coil for delivery to a spark plug.
Conventional capacitance discharge ignition systems are designed to deliver a fixed amount of energy to each spark plug to achieve a spark duration that will ignite the air/fuel mixture in the engine cylinder and sustain the flame for the desired combustion. However, it is well known that spark plug electrodes erode over a period of time, and that the energy needed for a desired spark duration increases as the spark plug erodes. Therefore, the energy delivered to the plugs in conventional ignition systems is set at a relatively high level to ensure that there is sufficient spark duration available to ignite the air/fuel mixture in the cylinder as the spark plug electrodes erodes within pre-defined limits. Unfortunately, delivering energy at a level that is higher than necessary to achieve the desired spark duration for the desired combustion has the effect of accelerating the spark plug erosion, and thus reducing the useful life of the spark plugs.
Another consideration in establishing the operating parameters of conventional ignition systems is the fact that the voltage required to ionize the fuel/air mixture between the electrodes of a spark plug changes as fuel/air mixture changes. As a result, conventional ignition systems are set to deliver excess energy to the spark plugs for anticipated worst-case operating conditions. This results in excessive spark plug erosion at operating conditions less than worst-case, further reducing the useful life of the spark plugs.
The consequences and costs associated with engine down-time to replace worn spark plugs, and the costs associated with the inefficiencies of operating spark plugs at less than the desired or optimal conditions is of particular concern in connection with engines that are utilized in industrial-type applications where the engines may be operating continuously for long periods of time. In fact, in many instances, the engines are intended to operate continuously except for repair-time. In addition to the fact that continuous operation logs substantial hours of operation relatively quickly, as compared with, for example, normal automotive uses, the useful life of spark plugs in some industrial engines are in the neighborhood of only hundreds of hours. In such instances, the losses and costs associated with operating the engine with a conventional ignition system adapted to provide excess energy to the spark plugs are quite substantial.